Ultrasonic generator



ARCH R SUBSTITUTE FOR MISSING XR July 13, 1965 A. NELKIN ETAL ULTRASONICGENERATOR 2 Sheets-Sheet 1 Filed Jan. 31, 1962 NGDAL DIAMETER d SECTOR ASECTOR c INVENTORS Anhur Nelkin Robert A. LesIer Roberf H. Whittaker8-IYohn H. Thompson ATTORNIZY wmuzssss: gLWWJ A. NELKIN ETAL ULTRASONICGENERATOR July 13, 1965 2 Sheets-Sheet 2 Filed Jan. 31, 1962 Unitedrates 3,194,209 ULTRASONIC GENERATOR Arthur Nelkin, Pittsburgh, RobertA. Lester, Pitcairn, Robert H. Whittaker, Export, and John H. Thompson,Pittsburgh, Pa., assignors to Westinghouse Electric Corporation, EastPittsburgh, Pa., a corporation of Pennsylvania Filed Jan. 31, 1962, Scr.No. 170,157 5 Claims. (Cl. 1l6137) The present invention relates to atransmitter for generating ultrasonic signals and more specifically to aflexural mode mechanical resonator to generate ultrasonic signals of thepredetermined frequency in the supersonic or ultrasonic range.

The requirements for usable mechanical resonators is that they canvibrate with sufficient amplitude and also sufficient duration. .Inaddition, if these resonators are to be used as ultrasonic transmittersthey must be capable of producing such signals of a frequency within arange of frequencies so that the ultrasonic receiver will be able toaccurately detect the transmitter signal despite various other signalswhich may be present. Such a desirable range would be in the order of 30kilocycles to 60 kilocyclcs where there is a minimum of extraneous soundsignals from such things as squeaky door hinges, ripping of paper, andalso a minimum of extraneous electromagnctic signals such as from radiostation transmitters, etc. Further in this frequency range the airabsorption is relatively low. In addition the resonator should berelatively small.

The types of vibration which bars or plates assume after they areactuated have been known for many years. Examples of various types ofmodes are illustrated in the book Acoustical Engineering" by Olsonpublished by D. Van Nostrand Co., 1957. Page 65 of this book illustratesvarious types of fiexural modes of a disc or plate while on page 67 ofthis book longitudinal vibrations of a rod are illustrated. 'Many of themodes illustrated in this book have been found unsatisfactory for use asa mechanical resonator or an ultrasonic transmitter either because thediscs, rods or plates cannot be or have not been satisfactorily mountedto provide sufficient output from the resonating element. Morespecifically, most heretofore known mounting means for many of theseresonators, absorbs most of the vibratory energy so that amplitude andring time of the vibrations or the resonating elements are very small.

A complete theory of the vibration of a plate suspended in air wasdescribed in a celebrated memoir by Kirchhoff in 1850. In this memoir,it was described that the gravest of all normal modes has no nodalcircle but rather vibrates with at least two nodal diameters in aflexural mode. It is stated in this memoir and other works that acircular plate and a square plate has its gravest mode with two nodallines that cross each other through the center of the circular or squareplate. Since the Kirchhoff grave mode is predicated upon a circularplate or square plate being suspended in air with no suspension orcontact or very little suspension contact, it has heretofore been foundto be impractical to utilize such a vibrating resonator for producingultrasonic signals.

Accordingly, it is an object of the invention to provide a new andimproved ultrasonic generator utilizing a flexural mode resonator havingat least two nodal diameters to generate ultrasonic signals of apredetermined frequency.

A further object of the invention is the provision of a 3,1942% PatentedJuly 13, 1965 new and improved Kirchhoff grave mode resonator forgenerating ultrasonic signals.

It is a still further object of the invention to provide a fiexural moderesonator in the form of a plate which can produce ultrasonic signals ofthe predetermined frequency having relatively large amplitude andduration.

An ultrasonic generator embodying the present invention includes aresonator which vibrates in a flexural mode with a plurality of nodaldiameters which diameters inter- Cept at a reference point to form anaxial reference through the resonator. A mounting pin is integral withthe plate and positioned concentric with the reference axis. The pinextends outwardly from the plate so that the vibrations of the platetravel a short distance down the integral pin and are cancelled so thatthere is no vibratory energy at the lower mounting portion of the pinand hence no energy is lost to the mounting. Means are applied to theouter edges of the plate to impart energy to the plate to initiateoscillations of. the flexural mode resonator. To further increase theoutput of the ultrasonic resonator, a housing is employed around theresonator and Is spaced parallel with the resonator surfaces a distancewherein is the wave length of the ultrasonic signals caused by thevibration of the resonator and N equals any integer or zero. Thishousing includes apertures therein so that the phase of the ultrasonicsignals coming out of the housing are substantially in phase whereas theenergy from the quadrants in the other phase of vibration are nottransmitted into space so as to prevent cancellation of the first namedphase vibrations.

These and other advantages of this invention will be more clearlyunderstood from the following description when read in conjunction withthe accompanying drawings in which:

FIG. 1 is an isometric exploded view of an assembly layout of anultrasonic generator constructed in accordance with the presentinvention;

FIG. 2 is a top view of the device illustrated in FIG. 1;

FIG. 3 is a cross-sectional view taken along lines III shown in FIG. 2;

FIG. 4 is a top view of the resonant plate illustrated in FIG. 1 withthe housing illustrated therein shown in dotted lines;

FIG. 5 is an isometric view of the resonant plate and mounting member ofthe resonator shown in FIG. 1;

FIG. 6 is a cross-sectional view of the mounting pin of the resonatorillustrated in FIGS. 1 through 5;

FIG. 7 is a side view of another embodiment of the invention; and,

FIG. 8 is an isometric view of a third embodiment of the invention.

FIG. 1 shows an assembled isometric view of an ultrasonic generatorconstructed in accordance with the present invention. This generatorcomprises generally a resonator 10 which is mounted on a base member 20.The resonator 10 shown is a plate, shown as circular in FIG. 1, whichwhen energy is imparted near the periphery thereof, will vibrate in aflcxural mode having at least two nodal diameters so as to provideopposite sectors on the plate which are in phase during vibration asshown in FIG. 4. As shown in FIG. 4, the plus sign indicates sectors Band D on the disc which will be traveling toward the viewer whereas thenegative sections A and C will be traveling away from the viewer atpoint in time during the vibration of the plate. This type of vibrationis characteristic of a resonator which is suspended in free aircontacting no other external structure. Ordinarily mounting such a plateto produce such a vibration absorbs such a great amount of the vibratoryenergy in the mounting means that ultrasonic signals transmitted to theair are negligible. In the present invention, however, a mounting meanswhich was found to produce or effect relatively large amplitude andduration vibrations is employed. The mounting means which enables one toutilize the vibration characteristic of an air suspended plate is a pinor mounting means which is integral with the vibratory plate. When sucha plate suspended in free air vibrates, the vibrations are described bynodal diameters al and (1 shown in FIG. 4. The diameters define sectorsof vibrations or movement up and down. These nodal diameters intersectat a vibratory reference point V on the plate and define a referenceaxis extending through and normal to the plate. The mounting pin forsuch a resonator is integral with the plate with the axis of the pinintersecting the above described reference axis at a point which is inthe plane of intersection of the two members. In this fashion, thesections of vibrations of the plate are transmitted down the integralpin so that the plus and minus vibrations or up and down vibrationstransmitted down the pin are equal and opposite and at some point beforethe mounting portion of the pin these vibrations are completely canceledso as to provide no transmission of energy outwardly from the pin.Hence, there is substantially no loss of energy from the resonatorexcept to the free air.

It has been discovered that in order to effect substantially no loss tothe mounting portion of the mounting pin, the mounting pin and theresonator must be integral and preferably made of the same piece ofmaterial as the plate. Integral, however, is not meant necessarily tomean that the pin is constructed from the same piece of material ormetal as the resonator but rather is meant to include any similarconnection such as where the pin is alloyed to the resonator.

A housing 30 is constructed around the disc and a striker means 40 issecured to the housing so as to impart energy to the disc to initiatevibrations thereof. The housing is spaced at odd quarter wave lengthsfrom the sides of the disc or the plate so as to effect storage ofenergy back to thedisc which it is not desired to utilize. As shown inFIG. 1, apertures are provided in the housing 30 which are oppositevibrating surfaces of the plate that are in phase and hence utilizingonly one phase of ultrasonic energy coming from the resonant disc 10.Still another aperture is provided in the housing which in theembodiment of FIG. 1 is a striker mounted on a spring to impartmechanical energy to the outer edges of the disc to initiateoscillations thereof.

In the embodiment of the invention illustrated in FIG. 1, the resonator10 comprises a circular disc 11 having an upper major surface 12 and alower major surface 13 with a circular outer peripheral side edge 14.Extending downwardly from the vibrating plate 11, as shown in FIG. 5, isan integral cylindrical pin 15 having a mounting portion withscrewthreads 16 at the free end thereof to define a mounting portion formounting the vibrator. The pin 15 is integral with the plate 11 and isconcentric with the periphery of the plate 11. In a preferred form foroptimum or greatest ultrasonic output, the pin 15 and the plate 11 areformed out of the same piece of material such as by constructing the pin15 by taking a cylindrical body and turning down one portion thereofwith a lathe to produce the pin 15.

The pin 15 is shown as extending from the lower major surface 13,however, a similar pin could also extend from the upper major surface12. Such a pin must also be integral with resonator 11 and concentricwith the reference axis described by the nodal diameters (1 and d FIG. 4illustrates a top view of the resonator 11. This view illustrates atypical tlcxural mode vibration of the disc which is describedby twonodal diameters 41 and 11 As shown in FIG. 4, when the plate 11vibrates, it will describe four vibrating sections A, B, C and D. Inthis configuration where'thc plate is a circular disc, these foursections are sectors. As shown in FIG. 4, sector A and sector C are inphase and are designated as such with a minus sign whereas the sector Band sector D are also in phase designated as such by a plus sign. Thatis, at a given point in time the sectors A and C are going away from theviewer whereas the sectors B and D are out of phase with the sectors Aand C and are coming up toward the viewer of the drawing. As can beunderstood, the maximum point of vibratory amplitude is in the center ofthe sectors and these vibrations are produced about the two nodaldiameters d and The vibration illustrated in FIG. 4 is descriptive of avibration of a circular disc which is in free air and has no structuralcontact with any other element. As described above, this is the gravestmode of a plate although as explained above, the problem of mountingsuch a vibratory system without losses to its support has heretoforebeen quite unsatisfactory. In addition, it is possible under someconditions and with certain dimensions and modulates of elasticity toproduce a flcxural mode of vibration where there is more than two nodaldiameters. The particular mounting means disclosed in the embodiment ofthe invention, however, will work satisfactorily with any fiexural moderesonator having at least two or more nodal diameters. Further theresonator can be a circular plate or cylinder or a square or rectangularplate or block.

The particular vibrations illustrated in FIG. 4 are produced byimparting energy such as by a mechanical striker or a piezoelectriccrystal, to either surface 12, 13 or 14. The point at which the energyis applied to the resonator determines the location of the nodaldiameters 11 and (1 with a, being 45 in one direction from this pointand d being 45 in the opposite direction from this point. In order toprovide a maximum of energy transfer from the actuating means, such as astriker mounted on a spring, the striker should hit the outer peripheraledge 14 or should hit the surfaces .12 and 13 of the vibrating plate 11near the periphery thereof. The closer the energy is applied to thecenter of the disc the less the amplitude and duration of thevibrations. If the energy is applied to the surface of the resonator ata point in actuating planes PI and P2 nodal diameters (l and (1 will beset up as shown in FIG. 4.

More specifically, when the disc is struck by a striker, this point onthe disc preferably substantially outwardly from the center of the disc,then sets up nodal diameters at 45 extending radially from the center ofthe device, from the point at which the energy was imparted to the disc.If the vibrating plate 11 is struck near the center thereof, very littlevibrating will be initiated since only a very small amount of thedeflection of the vibrating plate 11 will be effected.

When the disc or plate 11 commences to vibrate as shown in FIG. 4, thenodal diameters (f and (1 describe a point of vibratory reference 1' anda reference axis at the inner section thereof. On the lower majorsurface 13 of the disc 11, this point as projected on the lowermajorsurface is also the symmetrical center of the mounting pin 15 with theintersection of the disc 11. More specifically, the reference axis, inthe embodiment of the invention, is the center about which the in 15 ismounted on disc 11.

FIG. 6 illustrates the pin 15 with a cross section taken through theplane at which the pin 15 joins the lower major surface 13 of thevibratory plate 11.

The motion imparted to the pin 15 by the sectors A and C will be equaland opposite to the motion imparted by the pin body sectors B and D.Consequently, equal and opposite motions will oppose each other andcancel out a short distance down pin 15 so as to retain the energywithin the disc 11 and not allow this energy to be dissipated in themounting on the disc.

' it has been discovered that the pin must be integral with thevibratory plate 11. Forcing the pin into a hole on the disc 11 will notproduce satisfactory vibrations and much of the energy will bedissipated down through the mounting portion or threads 16 on the pin 15so as to provide an unsatisfactory resonator. In short, the pin 15 mustbe secured to the disc 11 in such a manner so that the transmission ofenergy down pin 15 by sectors B and D must be equal (and opposite) tothe energy transmitted up the pin 15 by the sectors A and C. This canonly be accomplished by having a continuity of material between the pin15 and the disc 11.

As shown in FIG. 1 and FIG. 3, the resonator 10 can be mounted by themounting portion having screw-threads 16 on a circular mounting disc 20having a threaded hole 21 in the center thereof. Threaded apertures orholes 22 are provided in the circular mounting base 20 to receive screwsfor mounting a housing 30. As will be explained later, this housingincreases the ultrasonic output of the resonator over and above the useof the resonator 10 in open air.

The housing 30 includes a cylindrical section 31 having holes forreceiving screws that will screw into the apertures 22 of the mountingbase 20. At the upper end of the housing 30 is a fiat planar top 32which is perpendicular to the cylindrical section 31. This top cover issecured to the cylindrical section 31 and has two diametrically opposedapertures 33 therein with another aperture 34 to provide an opening forthe actuating mechanism that imparts energy to the disc. As shown inFIG. 3, the actuating mechanism includes a leaf spring 41 having astriker 42 near the outer end thereof. The leaf spring 41 is secured tothe top cover 32 by a screw 43. The leaf spring 41 is of such aresiliency so that when the leaf spring is forced upwardly apredetermined distance lllC striker 42 will move into contact and impartone striking blow or tap to the resonant plate 11. to thereby initiateultrasonic output, the material of resonator 11 should have a Q of atleast 5,000 to 10,000. Some aluminum base metals as well as other metalshave Q5 of at least this amount.

Although the side walls of the housing are spaceda predetermineddistance from the resonator, there are, as shown in FIG. 1, twoapertures 33 in the top cover 32. These apertures in the top cover 32are located above sectors of vibration having the same phase since thehole 34 is 90 from hole 33. More specifically, as shown in FIGS. 4and 1. these apertures are located above sectors 13 and D. Hence,practically all the ultrasonic signals which come out of the housing 30are of the same phase. Consequently, cancellation due to opposite phaseof the signals coming from the vibrator to the free air is minimized.Although the hole 34 is to accommodate the striker 42 in the upper topplate 32 is over a sector A which is of the opposite phase of sectors Band D, there will be very little cancellation therefrom due to its beingcovered substantialy by the spring 41 and the striker 42. Hence, thehousing 30 enables the ultrasonic signals of the first phase describedemanating from sectors A and C to be effectively stored back in the discand without allowing them to effect any substantial cancellation of thesecond phase of the vibration emanating from the sectors B and D. Hencethe energy from the ultrasonic signals of the phase emanating fromsectors A and C is conserved and the output of the transmitter itselfwill be that of the energy having the second phase from the sectors 13and D.

Although the housing 30 as described above increases the ultrasonicoutput of the generator, the resonator 10 can be utilized without such areflective or resonant housing and still produce a substantialultrasonic signal such as shown in FIG. 7, the lower portion of pin 15is secured to a base having only a very small reflecting surface. Inaddition as shown in FIG. ii, energy can be transmitted to thevirbratory disc 11 by means other than a mechanical striker such as by apiezoelectric crystal which has an AC. applied thereto by a source 52through loads 51.

vibration therein. As will be understood, this striker 40 The frequencyof source 52 is the same as the resonant could be mounted to impart astriking force to either frequency of the resonator 11. The crystal issecured to the side edges 14 or the lower major surface 13 of. the thesurface of the vibrator 11 by some suitable conductftuexural disc orplate 11. When the resonator or transing adhesive. One of the leads 51is electrically conmitter is assembled as shown in FIG. 3, the mountingbase r nected to the upper side of crystal 50 and the other lead 20 isparallel to the lower major surface 13 of the flexural 51 iselectrically connected to the mounting pin 15. mode plate 11 a distanceS3 whereas the cylindrical section As stated previously, the mostdesirable frequency 31 of the housing 30 is spaced a distance S2 fromthe perange for ultrasonic signals is between 30 kilocyclcs and ripheraledges 14 of the vibrating plate. The top cover 32 kilocyclcs since inthis frequency hand there is a miniof the housing 30' is parallel to andspaced :1 distance S1 r mum of interference due to extraneouselectromagnetic from the upper major surface 12. These distances SI,waves and sonic waves. The following resonator was S2 and S3, foroptimum performance of the embodiment constructed with systems Qs infree air of about 35,000 illustrated in the drawings, are distanceswhich are odd made of 7075ST6 and 606lS-T6 aluminum discs. None quarterwave lengths of the frequency of vibration of the of these units lostany energy through the mounting porvibratory plate 11. More specificallythese distances S1, tion (the threaded portion of the pin 15). Nohousing S2 and S3 are equal to was employed in the tests on thesemodels. Other tests NA were made with housings and a substantial outputin- +7 crease was realized.

In these tables f is frequency of output. in kiloeycles, where N is anywhole integer (1,2, 3, 4 etc.) or zero. D is diameter of disc in inches,and r is thickness of disc In order for the resonator 11 to provide anyusable in inches.

TABLE I Data for 606lS-T6 aluminum dis/ts Mounting l'nlhreadml PointD/t; D. t, f, kc. f-D lt, fD, pin post. po t length, inches incheskc.-iu. kerin. 1lia.,in. in.(linl5) (Pin 15) 2. 5s 1.125 are its 57 .300.0113 4.0 1.02s 111.12 17s 44.3 .300 .219 4. 36 1.11s 37.0 ms 42. 1 .140.195 4.3a 1.11s 14am lss 43.2 .360 .1114 4.50 1.1511 31:.74 m 42.2 .3011.191 tan 1.500 25.5 ms 3x2 .360 .191 6.36 1.5110 10.8 2a.? .140 .305

Point D/t D, t, l, kc. LD /t, [1), Post dia., Post length,

inches inches kc.-in. ke.-in. in. in.

2.15 1. (115 37. (it) 12-4 59. 6 .1 10 250 3 1. 500 33.31 150 511.3.141) 151) 4 1. .25 40.61 lti'i '11. 7 Ht) 1!)? 4.35 1.118 35. U 170.839.1 Ht) .197 6. 5 1. 615 l 28. f 110 250 3 1. 500 51 50. l 2. 03 1. 29050. 6 3 1. 120 50. 3 2 1. r 02 N ,4 threaderl- 1. 5 1. 120 an gf' jjgff24" non 1 75 7 inch. scr. threaded While particular embodiments of theinvention have been shown and described, it is apparent thatmodifications and alterations may be made, to cover all suchmodifications as they fall within the true scope and spirit of theinvention.

We claim as our invention:

1. A mechanical resonator comprising, a vibrating plate resonant in afiexural mode with a plurality of nodal diameters, said plate having apair of parallel planar major surfaces with peripheral edge surfacesextending perpendicular to the planes of said major surfaces, acylindrical pin extending outwardly from one of said major surfaces andbeing concentric with said peripheral surfaces, said pin being integralwith said plate, and means for applying energy to said plate to actuatesaid plate into resonant vibration in a fiexural mode with a pluralityof nodal diameters.

2. A mechanical resonator comprising. a vibrating plate resonant in aflexural mode with a plurality of nodal diameters, said plate having apair of parallel planar major surfaces with peripheral edges extendingtherebetween, a pin extending outwardly from the center of one of saidmajor surfaces, said pin being integral with said plate, a reflectingsurface spaced from one of said major surfaces :1 distance equal towhere A equals the wave length of the ultrasonic waves produced by thesaid vibrating plate and N being any integer or zero, means for applyingenergy to said plate to actuate said plate into resonant vibration witha plurality of nodal diameters, said reflecting surface having anaperture therein with said aperture delining a projective surface onsaid one of said major surfaces with said projected surface beinglocated within an area between two adjacent nodal diameters.

3. A mechanical resonator comprising, a vibrating plate rcsonantin aflexural mode with a plurality of nodal diameters, said plate having apair of parallel planar major surfaces and an outer minor peripheralsurface transverse to the plane of said major surfaces, a circular pinextending outwardly from one of said major surfaces and concentrictherewith, said pin being integral with said circular plate, and meansfor applying energy to said plate near the outer periphery thereof toactuate said plate into resonant vibration in a flexural mode with -aplurality of nodal diameters.

4. A mechanical resonator comprising, a vibrating plate resonant in atlexural mode with a plurality of nodal diameters. said plate having amajor and a minor surfacewith said minor surface comprising theperipheral edges thereof, mounting means for said plate comprising amounting pin, means connecting said pin to the center of said majorsurface to apply equal and opposite vibratory forces to said pin, andmeans for applying energy to said plate to actuate said plate intoresonant vibration in a flexural mode with a plurality of nodaldiameters.

5. A mechanical resonator comprising. a vibrating late resonant in aflexttral mode with a plurality of nodal diameters, said plate having apair of parallel planar major surfaces with peripheral edge surfacestherebctwcen, a mounting pin, connecting means providing an undampcdconnection between said pin and the center of one of said majorsurfaces, and means for applying energy to said plate to actuate saidplate into resonant vibration in a fiexural mode with a plurality ofnodal diameters.

FOREIGN PATENTS 11/22 Germany. 1/24 Germany.

OTHER REFERENCES Publication, Grits and Grinds," January 1951, vol. 42,Issue 1, pages 1012.

LOUIS J. CAPOZI, Primary Examiner.

ARNOLD RUEGG, LEO SMILOW, Examiners.

1. A MECHANICAL RESONATOR COMPRISING, A VIBRATING PLATE RESONANT IN AFLEXURAL MODE WITH A PLURALITY OF NODAL DIAMETERS, SAID PLATE HAVING APAIR OF PARALLEL PLANAR MAJOR SURFACES WITH PERIPHERAL EDGE SURFACESEXTENDING PERPENDICULAR TO THE PLANES OF SAID MAJOR SURFACES, ACYLINDRICAL PIN EXTENDING OUTWARDLY FROM ONE OF SAID MAJOR SURFACES ANDBEING CONCENTRIC WITH SAID PERIPHERAL SURFACES, SAID PIN BEING INTEGRALWITH SAID PLATE, AND MEANS FOR APPLYING ENERGY TO SAID PLATE TO ACTUATESAID PLATE INTO RESONANT